JP2012040550A - Catalyst precursor dispersion, catalyst, and cleaning method of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst which can be industrially executed when manufacturing, which has proper sized micropores suitable for cleaning exhaust gas, and in which noble metal fine particles are carried only in the proper sized micropores of the carrier.SOLUTION: The catalyst is characterized by drying and sintering catalyst precursor dispersion characterized by including (A) carbon nanotubes carrying at least one noble metal particle or a noble metal oxide particle selected from the group comprising Ag, Ru, Rh, Pd, In, Os, Ir, and Pt and (B) a hydrated inorganic oxide.

Description

  The present invention relates to a catalyst precursor dispersion suitable for exhaust gas purification, a catalyst, and an exhaust gas purification method.

Conventionally, exhaust gas purification catalysts that purify harmful substances such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO _x ) contained in exhaust gas have been efficiently used with a small amount of noble metal. In order to purify the exhaust gas, it is required to increase the contact area between the catalyst and the exhaust gas. The following Patent Documents 1 to 3 have been reported as methods for producing a catalyst supported on a carrier having pores using carbon nanotubes, carbon nanohorns or carbon fibers.

  In the invention described in Patent Document 1, after a composite oxide is supported on carbon nanotubes, the carbon nanotubes are burned off to form a catalyst-supporting base material (support) having pores of about 1 to 10 nm. By mixing the supporting base and the catalyst component solution and applying high pressure, a catalyst in which the catalyst component is supported up to the deep part of the pores is obtained. However, the invention described in Patent Document 1 is not preferable as an exhaust gas treatment catalyst because the pore diameter is too small. In addition, the process is complicated, and in order to support the catalyst metal, it must be supported at a high pressure, and industrial implementation is difficult.

  In the invention described in Patent Document 2, a cluster-sized noble metal is introduced into carbon nanohorn, mixed with γ-alumina, etc., dried and incinerated to burn and remove carbon nanohorn to produce a supported catalyst. Yes. However, since the invention described in Patent Document 2 introduces metal into pores such as carbon nanohorns, it is necessary to raise the temperature considerably in a vacuum, which is also difficult to implement industrially. Further, this method cannot be said to have a pore volume and a pore diameter suitable as an exhaust gas treatment catalyst.

  The catalyst described in Patent Document 3 is prepared by adhering a slurry obtained by mixing carbon fibers and an inorganic material to a honeycomb carrier and firing the mixture. During the firing, the carbon fiber is incinerated, and a catalyst carrier in which minute continuous elongated cavities are formed. However, carbon fibers have a relatively large diameter and cannot be said to be a honeycomb carrier having pores suitable for an exhaust gas treatment catalyst. In addition, after that, noble metal is supported on this honeycomb carrier by impregnation method to make an exhaust gas treatment catalyst. In this method, the catalyst is supported not only on the pore surface where the carbon fiber disappeared but also on the fine pores originally possessed by the inorganic material. It cannot be said that noble metals are supported only in appropriate pores effective for combustion.

  Since a noble metal such as platinum (Pt) or palladium (Pd) is used as the exhaust gas purifying catalyst, it is necessary to increase the ratio of the noble metal that contributes efficiently to the reaction in order to reduce the amount of expensive catalyst noble metal. . For that purpose, it is necessary to form many pores suitable for combustion of exhaust gas containing various unburned components, and to dispose the catalyst noble metal only on the inner surface of the pores.

JP 2005-46669 A JP 2003-181288 A JP 63-205143 A

  In order to increase the surface area of the catalyst metal, that is, to reduce the size of the catalyst metal particles, it is conceivable to use the pores of the carrier, but if the pores of the carrier are too small, particles contained in the exhaust gas, etc. Clogged the pores of the carrier, and the catalyst was not able to function.

  Therefore, the problem to be solved by the present invention is that industrial implementation is easy at the time of production, has pores of an appropriate size suitable for exhaust gas purification, and has an appropriate size of pores of the carrier. It is only to provide a catalyst on which noble metal fine particles are supported.

  As a result of intensive studies, the present inventors have found that the above problem can be solved by preparing a catalyst using carbon nanotubes and a specific inorganic oxide, and have completed the present invention. The main points of the present invention are as follows.

(1) (A) Carbon nanotube carrying at least one kind of noble metal particles or noble metal oxide particles selected from the group consisting of Ag, Ru, Rh, Pd, In, Os, Ir and Pt, and (B) inorganic oxidation A catalyst precursor dispersion comprising a hydrate.
(2) (A) Carbon nanotube carrying at least one noble metal particle or noble metal oxide particle selected from the group consisting of Ag, Ru, Rh, Pd, In, Os, Ir and Pt, (B) inorganic oxidation A catalyst precursor dispersion liquid comprising a hydrate of hydrate and (C) at least one inorganic compound particle selected from the group consisting of alumina, silica, titania, zirconia and ceria-zirconia.
(3) A catalyst obtained by drying and calcining the catalyst precursor dispersion liquid according to (1) or (2).
(4) A catalyst characterized in that the catalyst precursor dispersion according to (1) or (2) is coated on a carrier and then baked to burn out carbon nanotubes.
(5) The catalyst according to (4), wherein the carrier is made of metal.
(6) The catalyst according to (5), wherein the metal carrier has an inorganic oxide on the surface.
(7) The catalyst according to (5) or (6), wherein the metal carrier is stainless steel containing aluminum.
(8) The catalyst according to any one of (5) to (7), wherein the support has a wire mesh shape.
(9) A method for purifying exhaust gas, characterized in that the catalyst according to any one of (3) to (8) is used.

  According to the present invention, when preparing a catalyst, industrial implementation is easy, and a catalyst in which a noble metal is supported on a support having moderately-sized pores suitable for exhaust gas purification can be obtained. Since the catalyst has high catalytic activity, the amount of expensive noble metal can be reduced.

The schematic diagram of the catalyst of this invention. The expansion schematic diagram of the catalyst of this invention. Sectional TEM photographic image of the catalyst of Example 2 (magnification 40000 times). 6 is a graph showing a pore distribution curve of the catalyst of Example 4. Reaction vessel used for the catalytic activity test. The graph which shows the result of a catalyst activity test (carbon monoxide oxidation reaction). The graph which shows the result of a catalyst activity test (propylene oxidation reaction).

<Catalyst precursor dispersion>
The catalyst precursor dispersion in the present invention is a dispersion containing a component that is a catalyst raw material (for exhaust gas purification) of the present invention, and includes components (A) Ag, Ru, Rh, Pd, In, Os, It consists of a carbon nanotube (hereinafter abbreviated as CNT) carrying at least one kind of noble metal atom selected from Ir and Pt and a component (B) inorganic oxide hydrate. The catalyst precursor dispersion of the present invention includes those that become uniform by stirring even if there are components that settle and separate upon standing.

  The CNT of component (A) further includes a promoter component commonly used for improving activity and preventing sintering, etc., Ni, Co, Mg, Fe, Hf, W, V, Mo, Ti, Re, Ta, Nb, alkali metal / alkaline earth metal or the like may be supported.

  As the CNT carrying the noble metal, any of SWCNT (single layer), DWCNT (double layer), and MWCNT (multilayer) can be used. Although it is not limited to the shape, in order to bring out the characteristics of carrying precious metal particles, performing a baking process, and forming pores of submicron to micrometer size, the diameter is 2 nm or more and the length is 100 nm to 10 μm. Something like that is preferable. In addition, there are various methods for producing CNT, such as a CVD method and an arc discharge method, and any method can be selected. For example, the method described in Carbon Vol.35 No10-11, pp1495-1501,1997 Can be created.

  As the noble metal supported on the CNT, at least one kind of noble metal selected from Ag, Ru, Rh, Pd, In, Os, Ir, and Pt, which is usually used as an exhaust gas purification catalyst, is used. The smaller the size of the noble metal supported on the CNTs, the greater the surface area of the catalyst, which is preferable, but the particle size is preferably 1 to 100 nm, particularly about 1 to 50 nm. The specific surface area is very small, making it difficult to increase the activity of the catalyst.

As a method for supporting noble metal particles or noble metal oxide particles (having a plurality of noble metal elements and a plurality of valence structures in an aggregate of 1 to 100 nm size noble metal oxide) on CNT,
(1) A method in which CNT is dispersed in a solvent, a noble metal salt is dissolved therein, and then neutralized with an alkali to be fixed as a noble metal hydroxide on the CNT, followed by reduction treatment or oxidation treatment by heat treatment,
(2) Method of supporting noble metal oxide on CNT by mixing CNT and noble metal hydroxide or noble metal oxide in a solvent, then concentrating, drying and heat treatment (3) Mixing CNT and noble metal salt in solution After that, the noble metal salt is supported on the CNTs by concentration and drying, followed by heat treatment under conditions where the CNTs are not oxidized, and there is a method of making the noble metal salt a metal or metal oxide, metal composite oxide fine particles, etc. It is not limited to these methods.

  The amount of the noble metal supported on the CNT is not particularly limited, but is 0.1 to 20 wt%, preferably 1 to 10 wt% with respect to the CNT. When the amount is less than 0.1 wt%, the amount of noble metal is too small, so that the effect as a catalyst cannot be sufficiently exhibited. On the other hand, when it exceeds 20 wt%, the noble metal is difficult to be supported on the CNT, and even if it can be supported, the noble metal particles are likely to come off, and the noble metal particles may be easily sintered.

  As the component (B), at least one selected from alumina hydrate, alumina silica hydrate, silica hydrate, titania hydrate, zirconia hydrate, hafnia hydrate and ceria zirconia hydrate. Inorganic oxide hydrates are preferred.

  The component (B) is preferably added in a state of being dispersed in a suitable dispersion medium such as an inorganic oxide hydrate sol. As the dispersion medium, water that can be efficiently dried and removed, methanol, ethanol, and the like can be used. Water-soluble alcohols are preferred, and water is particularly preferred.

  The component (B) becomes an inorganic oxide when baked, and serves as a carrier and as a binder for binding other components.

  Furthermore, the catalyst precursor dispersion of the present invention may contain inorganic compound particles as the component (C). The component (C) is preferably at least one inorganic compound particle selected from alumina, silica, zirconia, titania and ceria particles. The particle diameter is preferably 10 nm to 100 μm.

  The solid content in the catalyst precursor dispersion, that is, the CNT supporting the catalyst noble metal, the inorganic oxide hydrate, the inorganic compound particles, etc. is 5 to 25% by weight with respect to the amount of the catalyst precursor dispersion. Prepare as follows. If the solid content contained in the catalyst precursor dispersion is lower than 5% by weight, the dispersibility of the solid component in the catalyst precursor dispersion is deteriorated and it is difficult to make it uniform. If it exceeds 25% by weight, the viscosity of the catalyst precursor dispersion becomes too high, and the operability during coating becomes poor.

<Catalyst>
Catalyst production method
What is a catalyst obtained by drying and calcining a catalyst precursor dispersion?
(1) The catalyst precursor dispersion is dried, (2) the inorganic compound particles and the inorganic compound hydrate are immobilized by firing at a temperature at which the CNT does not disappear, and (3) the CNT is lost. Thus, the noble metal particles carried on the CNTs are arranged on the edge of the holes created by the disappearance of the CNTs.

  (1) When drying the solvent of the catalyst precursor dispersion, it is preferably dried at about 50 to 200 ° C. for about 1 to 24 hours. In that case, it is possible to dry under reduced pressure. A freeze-drying method can also be used. Heating to 200 ° C. or higher is not preferable because the uniformity of the medium is not maintained and the alumina layer and the CNT layer are separated.

  (2) When immobilizing inorganic compound particles and inorganic compound hydrate by firing at a temperature at which CNT does not disappear, it is preferably fired at 300 ° C. to 400 ° C. for about 1 hour to 3 hours. When the calcination temperature is higher than 400 ° C., the noble metal functions as an oxidation catalyst and there is a possibility that CNTs are burned. On the other hand, when the calcination temperature is lower than 300 ° C., the immobilization on the carrier becomes insufficient, and when the catalyst is prepared, noble metal particles can be detached and appropriate pores cannot be obtained.

  (3) When CNTs disappear, it is preferable to fire at 600 ° C. to 900 ° C. for about 1 hour to 10 hours. When the calcination temperature is 600 ° C. or higher, the disappearance of CNTs is noticeable, and below that, CNTs may remain in the catalyst. On the other hand, when the temperature is 900 ° C. or higher, the supported metal particles are likely to be sintered or detached from the catalyst surface.

After the catalyst precursor dispersion is supported on a carrier, the dried and calcined catalyst is
(1) The carrier is coated with the catalyst precursor dispersion, (2) the solvent of the catalyst precursor dispersion is dried, and (3) the inorganic compound particles and the inorganic compound are baked at a temperature at which CNT does not disappear. After fixing the hydrate, (4) the noble metal particles supported on the CNTs by annihilating the CNTs are arranged at the edges of the pores created by the disappearance of the CNTs.

  (1) Examples of the material for the carrier on which the catalyst precursor dispersion is coated include a metal carrier. Among metal carriers, stainless steel materials are preferred because of their excellent heat resistance and strength. Further, when the surface of the support is covered with an inorganic oxide, the adhesion with the inorganic oxide hydrate contained in the catalyst precursor dispersion is excellent. As a method of creating a material whose surface is covered with an inorganic oxide, for example, a method of forming an alumina layer on the surface by heat-treating stainless steel containing aluminum as described in JP-A-2005-095846 is exemplified. It is done.

  As the shape of the carrier, a shape that increases the contact area with the exhaust gas and does not significantly impede the flow of the gas is good, and is spherical, cylindrical, single or multistage having a diameter of about 0.1 mm to 10 mm. The network structure is preferable.

  As a method for coating the carrier with the catalyst precursor dispersion, any method can be used as long as it is a usual method, and examples thereof include a dipping method, a roller method, a brush method, a spray method, and a spin method. The thickness of the coating is preferably about 100 nm to 500 μm. If it is less than 100 nm, it is thinner than the size of the inorganic compound particles contained in the coating solution, so that a flat catalyst precursor film cannot be formed, and if it exceeds 500 μm, the catalyst precursor film tends to peel off from the carrier. Therefore, it is not preferable.

  The structure of the catalyst of the present invention is schematically shown in FIGS.

  When the catalyst precursor dispersion or the catalyst precursor dispersion coated on the carrier is dried and calcined, the inorganic oxide hydrate of component (B) becomes an inorganic oxide, and the whole catalyst is fixed, and the binder of 3 A layer is formed.

  Further, CNT disappears by firing, so that holes as shown in FIG. 1 are formed. As shown in FIG. 2, the noble metal particles 4 supported on the surface of the CNT are arranged at an appropriate interval at the edge of the hole 1.

  Since actual CNTs are somewhat agglomerated or bundled in the coating solution, pores (submicron to micron size) larger than the fiber diameter (nanosize) of CNTs may be formed.

  When the pore distribution of the catalyst of the present invention is measured, there are two peaks: fine pores derived from inorganic compound particles and inorganic compound hydrates contained in the catalyst, and pores formed after CNTs are lost. Measured. A pore peak of pores formed after CNT disappears appears at 100 nm or more.

  In the method of purifying exhaust gas, a catalyst is installed at a predetermined position for purifying exhaust gas, and exhaust gas is flowed. At that time, if the temperature of the exhaust gas is lowered too much, the activity of the catalyst is lowered. Therefore, the exhaust gas is preferably installed at a position where the temperature of the exhaust gas is not lowered. Moreover, since the internal pressure of an engine etc. will rise if the flow rate of exhaust gas becomes too slow, it is preferable to install in a position that does not hinder the flow rate of exhaust gas.

The following measurement apparatus was used.
Specific surface area of catalytic metal m ² / g (Nippon Bell, BEL-METAL-3)
It was measured by a flow-type specific surface area automatic measuring device (trademark “Flowsorb II2300”, Micrometrics Instrument Co.).

Pore size
Using a mercury intrusion porosimeter (Autopore IV9500, manufactured by MICROMERITICS), the pore distribution in the range of 0.0018 μm to 100 μm is measured. The maximum point is defined as the peak top pore diameter from the pore distribution curve.

Average particle size
Specific surface area of metal
The degree of CO adsorption was measured with a metal dispersion measuring device (BEL-METAL-3, Nippon Bell Co., Ltd.), and the average particle diameter of the noble metal and the surface area of the noble metal on the catalyst surface were calculated.

Metal crystallite diameter
Using a X-ray diffractometer (RINT2100, Rigaku Corporation), the sample was measured in the range of 2θ = 30-60 °, and the crystallite diameter was calculated from the half-width of the peak corresponding to palladium oxide near 2θ = 34 °. did.

Analysis of Exhaust Gas HC, CO, and CO ₂ were measured with an exhaust gas measuring instrument (MEXA-584L, Horiba, Ltd.).

Production Example 1
(Production of 10% Pd (II) -CNT)
To a 500 mL four-necked flask, 3.0 g of CNT (prepared by the method described in Carbon Vol.35 No10-11, pp1495-1501, 1997) and 50 mL of distilled water were added and stirred for 5 minutes. Subsequently, 6 mL of a palladium nitrate solution (palladium concentration 50 g / L) was added to the flask with stirring. After stirring at room temperature for 30 minutes, the water was distilled off under reduced pressure using an evaporator to obtain 3.6 g as a concentrated residue. This concentrate was transferred to a magnetic crucible, dried at 100 ° C. for 1 hour in a dryer, and then baked at 350 ° C. for 1 hour in an electric furnace purged with nitrogen to obtain 3.1 g of 10% Pd-CNT. It was.

Example 1
Polyester of 2.0 g of 10% Pd (II) -CNT produced, 158.0 g of alumina sol (product name: Aluminum sol-10A, manufactured by Kawaken Fine Chemicals Co., Ltd., 10.0% pure alumina), 50 g of zirconia balls (φ2 mm) The catalyst precursor dispersion liquid was obtained by putting into a container and processing for 1 hour at 50 Hz using a rocking mill (SEIWAGIKEN ROCKING MILL).

Example 2
The catalyst precursor dispersion obtained in Example 1 was concentrated under reduced pressure, followed by drying at 100 ° C. for 2 hours in a drier, baking at 400 ° C. for 2 hours in an electric furnace purged with nitrogen, and further baking at 800 ° C. for 2 hours. As a result, 15.1 g of a 1.25% Pd (II) -alumina catalyst was obtained.

  FIG. 3 is a TEM image of the catalyst obtained in Example 2. It can be seen that Pd particles 4 are arranged on the edge of the pores 1.

Example 3
3.1 g of 10% Pd (II) -CNT produced in Production Example 1, 14.0 g of alumina sol (Product name: Aluminum sol-10A, manufactured by Kawaken Fine Chemicals Co., Ltd., 10.0% pure alumina), γ-alumina 23 .1 g (Rhodia, average particle size 22-23 μm), distilled water 100 mL, zirconia balls (φ2 mm) 50 g were put in a plastic container and treated with a rocking mill (SEIWAGIKEN ROCKING MILL) at 50 Hz for 1 hour to produce a catalyst. A precursor dispersion was obtained.

Example 4
The catalyst precursor dispersion liquid obtained in Example 3 was put in a stainless steel vat and dried at 100 ° C. for 2 hours with a dryer to obtain 24.3 g as a solid. After crushing the obtained solid, 24.3 g was weighed into a magnetic crucible and baked at 400 ° C. for 1 hour in an electric furnace purged with nitrogen to obtain 22.3 g. Furthermore, it was calcined at 800 ° C. for 1 hour in an electric furnace to obtain 19.7 g of a 1.25% Pd (II) -alumina catalyst.

Comparative production example 1
Distilled water 100 mL, γ-alumina (manufactured by Rhodia, average particle size 22-23 μm) 46.2 g, palladium nitrate solution (palladium concentration 50 g / L) 12 mL were added to a 500 mL four-necked flask and stirred at room temperature for 1 hour. The water was distilled off under reduced pressure using an evaporator, then transferred to a stainless steel vat and dried in a dryer at 100 ° C. for 15 hours to obtain 44.8 g as a tan powder. The obtained powder was transferred to a magnetic crucible and baked for 1.5 hours at 400 ° C. in an electric furnace to obtain 43.0 g of 1.28% Pd (II) -alumina. (Alumina supported catalyst)

Comparative Example 1
Pd (II) -alumina 23.1 g produced in Comparative Production Example 1, CNT 3.0 g, 10% alumina sol solution (Product name: Alumina sol 10A, manufactured by Kawaken Fine Chemical Co., Ltd., pure content 10.0%) 6.0 g Then, 100 mL of distilled water and 50 g of zirconia balls (φ2 mm) were placed in a plastic container and treated with a rocking mill at 50 Hz for 1 hour to uniformly disperse. This dispersion was put in a stainless steel vat and dried in a dryer at 100 ° C. for 2 hours to obtain 27.7 g as a solid. After crushing the obtained solid, 27.5 g was weighed into a magnetic crucible and baked at 400 ° C. for 2 hours in an electric furnace purged with nitrogen to obtain 22.6 g. Further, it was calcined at 800 ° C. for 1 hour in an electric furnace to obtain 21.3 g of a 1.25% Pd (II) -alumina catalyst.

Comparative production example 2
CNT 3.0 g, γ-alumina 23.1 g, 10% alumina sol solution (product name: alumina sol 10A, manufactured by Kawaken Fine Chemical Co., Ltd., pure content 10.0%) 6.0 g, acetic acid 6.6 g, distilled water 100 mL, 50 g of zirconia balls (φ2 mm) was put in a plastic container and treated with a rocking mill at 50 Hz for 1 hour to uniformly disperse. This dispersion was placed in a stainless steel vat and dried at 100 ° C. for 2 hours with a dryer to obtain 22.3 g of a solid. The obtained solid was crushed, transferred to a magnetic crucible, and baked at 350 ° C. for 2 hours in an electric furnace purged with nitrogen. Further, it was baked at 800 ° C. for 2 hours in an electric furnace to obtain 18.3 g of porous alumina.

Comparative Example 2
18.0 g of alumina produced in Comparative Production Example 2, 200 mL of distilled water and 4.6 mL of palladium nitrate solution (palladium concentration 50 g / L) were added to a 500 mL four-necked flask, stirred at room temperature for 1 hour, and then reduced in pressure using an evaporator. Concentration gave 22.9 g as a pale yellow solid. 22.6 g of the obtained powder was weighed into a magnetic crucible and baked at 400 ° C. for 2 hours in an electric furnace purged with nitrogen to obtain 17.4 g. Further, it was calcined at 800 ° C. for 1 hour in an electric furnace to obtain 17.2 g of a 1.25% Pd (II) -alumina catalyst.

Comparative Example 3
1.28% Pd (II) -alumina 10.0 g produced in Comparative Production Example 1 10% alumina sol solution (product name: alumina sol 10A, pure content 10.0%) 2.6 g, distilled water 80.0 g, zirconia 50 g of balls were put in a plastic container and treated at 50 Hz for 1 hour using a rocking mill to uniformly disperse. The dispersion was placed in a stainless steel vat and dried at 100 ° C. for 2 hours to obtain a solid. The solid was transferred to a magnetic crucible and calcined in an electric furnace at 400 ° C., 400 ° C. for 2 hours, and further calcined at 800 ° C. for 2 hours to obtain 9.12 g of a 1.25% Pd (II) -alumina catalyst. .

  Table 1 shows the physical properties of the catalysts prepared below.

  FIG. 4 shows a pore distribution curve of the catalyst of Example 4.

  For the catalyst containing CNT (Example 2, Example 4, Comparative Example 1, Comparative Example 2), two peaks appear in the pore distribution curve. It shows that small pores of alumina and relatively large pores formed after CNT disappears.

Production Example 2
Add 500 mL of distilled water, 10.0 g of CNT (same as above), 6.4 mL of palladium nitrate solution (palladium concentration 50 g / L), 27 mL of rhodium nitrate solution (rhodium concentration 3.0 g / L) to a 500 mL four-necked flask, Stir at room temperature for 1 hour. The water was distilled off under reduced pressure using an evaporator, then transferred to a magnetic crucible and dried at 100 ° C. for 2 hours in a drier. Furthermore, it was fired in an electric furnace under a nitrogen atmosphere at 400 ° C. for 2 hours to obtain 9.9 g of 3.2% Pd (II) -0.8% Rh (III) -CNT.

Example 5
2.0% of 3.2% Pd (II) -0.8% Rh (III) -CNT produced in Production Example 2, 2.0 g of γ-alumina, 10% alumina sol solution (product name: alumina sol 10A, pure content 10 0.0%) 180.0 g, distilled water 40 mL, acetic acid 5 g, and zirconia balls (φ2 mm) 50 g were placed in a 250 mL plastic container and treated with a rocking mill at 50 Hz for 1 hour to prepare a catalyst precursor dispersion. .

Example 6
The catalyst precursor dispersion of Example 5 was placed in a stainless steel vat and immersed in a ferritic stainless steel net (size 3 cm × 24 cm, 6.38 g) prepared by the method described in JP-A-2005-095846. Coated. Excess catalyst precursor dispersion was removed by blowing nitrogen gas. The coated net was dried at 100 ° C. for 2 hours in a drier and baked in an electric furnace at 400 ° C. for 2 hours. The same operation was repeated twice more. Next, calcination was carried out at 800 ° C. for 2 hours in an electric furnace, and the contained CNTs were calcinated and removed to obtain 6.66 g of a 0.32% Pd-0.08% Rh-alumina supported stainless mesh catalyst (catalyst support rate) : 3.89 mg / cm < ² >).

Comparative production example 3
Distilled water 100 mL, γ-alumina 10.0 g, palladium nitrate solution (palladium concentration 6.4 g / L) 50 mL, rhodium nitrate solution (rhodium concentration 3.0 g / L) 27 mL were added to a 500 mL four-necked flask at room temperature. Stir for hours. The water was distilled off under reduced pressure using an evaporator, then transferred to a magnetic crucible and dried at 100 ° C. for 2 hours in a drier. Furthermore, it baked at 400 degreeC for 2 hours with the electric furnace, and obtained 9.9g of 3.2% Pd-0.8% Rh-alumina.

  Produced 3.2% Pd (II) -0.8% Rh (III) -alumina 2.0 g, γ-alumina 2.0 g, 10% alumina sol solution (product name: alumina sol 10A, pure content 10.0%) 160.0 g, distilled water 40 mL, acetic acid 5 g, and zirconia balls (φ2 mm) 50 g were placed in a 200 mL plastic container and treated with a rocking mill at 50 Hz for 1 hour to prepare a catalyst precursor dispersion.

Comparative Example 5
The catalyst precursor dispersion of Comparative Production Example 3 was placed in a stainless steel vat and immersed in a ferritic stainless steel net (2.7 cm × 15 cm, 3.34 g) prepared by the method described in JP-A-2005-095846. Coated. Excess catalyst precursor dispersion was removed by blowing nitrogen gas. The coated net was dried at 100 ° C. for 2 hours in a drier and baked in an electric furnace at 400 ° C. for 2 hours. The same operation was repeated twice more. Next, it was calcined at 800 ° C. for 2 hours in an electric furnace to obtain 3.50 g of 0.32% Pd (II) -0.08% Rh (III) -alumina-supported stainless mesh catalyst (ratio of catalyst support: 3 .95 mg / cm ² ).

Catalyst activity test Exhaust gas discharged from a general-purpose engine was passed through a stainless steel pipe to which a catalyst can be attached, and the reduction rate of discharged hydrocarbon (hereinafter referred to as HC) and carbon monoxide (hereinafter referred to as CO) was examined. The general-purpose engine used was a 2-cycle engine attached to the Koyo Heidels pump KR-25S, and exhaust gas was analyzed during idling.

Total engine displacement: 24.5cc
Number of revolutions when idling: 3700 rpm
The gasoline used was a mixed gasoline (for 2-cycle engine) manufactured by Cainz Co., Ltd. 25: 1.

For the analysis of exhaust gas, simultaneous analysis of HC, CO, and CO ₂ was simultaneously performed using an automobile exhaust gas analyzer MEXA-584L manufactured by Horiba.

Noble metal content in one catalyst: 65.6 μg (Pd: 49.2 μg, Rh: 16.4 μg)
The catalytic combustion treatment effect of the catalyst when the HC ratio is reduced by 0.5% is estimated to be 135 liters per minute (HC) / g (noble metal).

  The combustion treatment effect of the catalyst when the CO ratio is reduced by 3% is estimated to be 809 liters (CO) / g (noble metal) per minute.

Comparative Example 6
(Blank test using exhaust gas)
Heidels pump KR-25S (manufactured by Koshin Co., Ltd., hereinafter abbreviated as “pump”) is operated and adjusted to 3700 rpm (± 50 rpm) with a tachometer, and then exhaust gas analysis is performed. It was. The exhaust gas was passed through a stainless steel tube having an inner diameter of 2.4 mm, the internal temperature was measured, and analysis of the gas exhausted from the stainless steel tube was measured with MEXA-584L.

Example 7
The pump was operated under the same conditions as in Comparative Example 6, and the catalyst activity test was performed using the exhaust gas discharged. One catalyst of Example 6 cut out to a diameter of 2.3 cm was arranged perpendicularly to the flow rate direction of the exhaust gas, and the composition change of HC, CO, CO ₂ in the exhaust gas was measured with a gas analyzer. Each measured value was measured 3 minutes after confirming that the thermometer immediately before the catalyst reached a predetermined temperature (exhaust gas temperature).

Example 8
Exhaust gas was measured in the same manner as in Example 6 except that two catalysts of Example 6 cut out to a diameter of 2.3 cm were arranged perpendicular to the flow rate direction of the exhaust gas.

Comparative Example 7
Exhaust gas was measured by the same method as in Example 7 except that a stainless mesh cut out to a diameter of 2.3 cm was used.

Comparative Example 8
It implemented by the same method as Example 7 except having used the catalyst created by the comparative example 5 cut out to diameter 2.3cm.

  Usually, in order to increase the activity of the catalyst, the average particle diameter and the crystallite diameter are reduced, and the specific surface area of the noble metal is increased to increase the catalytic activity. However, as can be seen from Table 1, in the present invention, the specific surface area of Pd is lower than that of the comparative example, and the average particle diameter and crystallite diameter are higher than those of the comparative example. That is, the physical properties opposite to those required by ordinary catalysts are exhibited. However, the activity of the catalyst of the present invention shows the same or better ability than the catalyst of the comparative example. This is because the catalyst of the present invention does not exist in the fine pores where the exhaust gas cannot enter, but exists only in the pores created by the disappearance of the CNTs.

Production Example 3
(Production of 10% Pd (0) -CNT)
10.0 g of CNT and 300 mL of distilled water were added to a 1 L four-necked flask and stirred for 1 hour. Subsequently, 8.0 g of sodium carbonate was added to the flask with stirring, and the mixture was stirred at room temperature for 1 hour. Further, an aqueous palladium chloride solution (palladium content 1.15 g) was slowly added, followed by stirring for 12 hours. After heating at 80 to 90 ° C. for 1 hour, the mixture was once cooled to room temperature, 2.5 g of sodium formate was slowly added, and the mixture was heated at 80 to 90 ° C. for 1 hour. Then, after cooling to room temperature, the catalyst was filtered using a Kiriyama funnel and further washed with 2 L of water. The filtered catalyst was dried in a dryer at 100 ° C. for 12 hours to obtain 11.8 g of 10% Pd (0) -CNT.

Example 9
The 1.25% Pd (II) -alumina catalyst prepared in Example 4 was combed and adjusted to a 20-40 mesh size, and air (10% water) was passed through an electric furnace at 1000 ° C. for 24 hours. After the aging treatment, a catalytic activity test described later was conducted using 0.6 g.

Example 10
Using the same method as in Example 3 and Example 4 except that 10% Pd (0) -CNT prepared in Production Example 3 was used instead of 10% Pd (II) -CNT in Example 3. A 25% Pd (0) -alumina catalyst was prepared. The catalyst was sieved, adjusted to a 20-40 mesh size, subjected to an aging treatment in the same manner as in Example 9, and then a catalytic activity test described later was conducted using 0.6 g.

Example 11
1% Pd (II) -CNT was prepared in the same manner as in Production Example 1 except that the palladium concentration in palladium nitrate was changed from 50 g / L to 5 g / L in the production method of Pd (II) -CNT in Production Example 1. Created.

  From 1% Pd (II) -CNT 2.0 g, γ-alumina 10.0 g, 10% alumina sol solution (product name: alumina sol 10A, pure content 10.0%) 9.0 g, distilled water 70 mL, acetic acid 0.5 g Using the same method as in Example 3 and Example 4, 9.5 g of 0.2% Pd (II) -alumina catalyst was prepared. The catalyst was sieved, adjusted to a 20-40 mesh size, subjected to an aging treatment in the same manner as in Example 9, and then a catalytic activity test described later was conducted using 0.6 g.

Example 12
0.4 g of 1% Pd (II) -CNT prepared in Example 11, 1.6 g of CNT, 19.0 g of γ-alumina, 10.0 g of 10% alumina sol solution (product name: alumina sol 10A, pure content 10.0%), Using 70 mL of distilled water and 0.5 g of acetic acid, 9.5 g of 0.02% Pd (II) -alumina catalyst was prepared in the same manner as in Example 3 and Example 4. The catalyst was sieved, adjusted to a 20-40 mesh size, subjected to an aging treatment in the same manner as in Example 9, and then a catalytic activity test described later was conducted using 0.6 g.

Example 13
The catalyst prepared in Example 12 was sieved and adjusted to a 20-40 mesh size, and after aging treatment was performed in the same manner as in Example 9, a catalytic activity test described later was performed using 0.3 g. .

Production Example 4
(3.8% Pd (II) -0.2% Rh (III) -CNT)
Add 200 mL of distilled water, 10.0 g of CNT (same as above), 7.6 mL of palladium nitrate solution (palladium concentration 50 g / L), and 6.7 mL of rhodium nitrate solution (rhodium concentration 3.0 g / L) to a 200 mL four-necked flask. And stirred at room temperature for 1 hour. The water was distilled off under reduced pressure using an evaporator, then transferred to a magnetic crucible and dried at 100 ° C. for 2 hours in a drier. Furthermore, it was baked at 400 ° C. for 2 hours in an electric furnace under a nitrogen atmosphere to obtain 9.8 g of 3.8% Pd (II) -0.2% Rh (III) -CNT.

Example 14
3.8% Pd (II) -0.2% Rh (III) -CNT 5.0 g produced in Production Example 4, cerium (IV) oxide (particle diameter 25 nm or less) 0.87 g, zirconia (IV) oxide ( (Particle size 100 nm or less) 2.47 g, γ-alumina 12.1 g, 10% alumina sol solution (product name: alumina sol 10A, alumina pure 10.0%) 4.0 g, distilled water 100 mL, acetic acid 0.23 g Using a method similar to Example 3 and Example 4, 14.1 g of a 1.19% Pd (II) -0.06% Rh (III) -alumina catalyst was made. The catalyst was sieved, adjusted to a 20-40 mesh size, subjected to an aging treatment in the same manner as in Example 9, and then a catalytic activity test described later was conducted using 0.6 g.

Comparative Example 9
0.2% Pd (II) -alumina was prepared in the same manner as Comparative Production Example 1 except that the palladium concentration of the palladium nitrate solution of Comparative Production Example 1 was changed from 50 g / L to 5 g / L.

  The 0.2% Pd (II) -alumina 1.0 g, γ-alumina 8.5 g, 10% alumina sol solution (product name: alumina sol 10A, pure content 10.0%) 5.0 g, distilled water 70 mL, acetic acid 0 9.4 g of 0.02% Pd (II) -alumina catalyst was prepared from 0.5 g using the same method as in Example 3 and Example 4. The catalyst was sieved, adjusted to a 20-40 mesh size, subjected to an aging treatment in the same manner as in Example 9, and then a catalytic activity test described later was conducted using 0.3 g.

Comparative Example 10
After powdery γ-alumina (Rhodia, average particle size 22-23 μm) was pressure-molded into a plate shape, crushing and sieving were performed to adjust the size to 20-40 mesh. A catalytic activity test described later was conducted on 0.6 g of the γ-alumina whose size was adjusted.

(Catalyst activity test using automobile model exhaust gas)
The catalysts prepared in Examples 9 to 14 and Comparative Examples 9 to 10 were filled in the central portion 12 of a quartz glass cylindrical reaction vessel (inner diameter 17 mm) 11 shown in FIG. The reaction vessel is fixed perpendicular to the ground, and gas flows from top to bottom. The gas used is a mixed gas consisting of oxygen 8.0%, carbon dioxide 10.3%, propylene 2,700 ppm (carbon conversion), carbon monoxide 900 ppm, moisture 10%, and nitrogen (residue), and the gas flow rate. Was allowed to flow from the top of the reaction vessel at 2,000 mL / min. Heated by an electric furnace installed outside, the temperature is measured at the tip of a thermocouple tube 15 installed in the center of the reaction vessel.

Change the temperature in the vessel at a rate of temperature rise of 5 ° C / min in the range of 100 to 400 ° C, flow mixed gas, and change over time of the oxidation reaction of propylene and the oxidation of carbon monoxide from the gas discharged from the lower part of the reaction vessel Tracked. Propylene and carbon monoxide are analyzed using an infrared spectrum measuring apparatus (NEXUS 670-FTIR manufactured by Nicolet). Propylene (measurement wavelength: 912 cm ⁻¹ ) and carbon monoxide discharged from the reaction vessel The content of (measurement wavelength: 2,158 cm ⁻¹ ) was measured.

  The results are shown in FIGS.

  It was found that the catalyst of the present invention was more active at a lower temperature than the comparative example.

  According to the present invention, a catalyst suitable for exhaust gas purification can be easily produced industrially, which is extremely useful from the viewpoint of environmental protection.

1: pores formed in disappearance trace of CNT 2: carrier 3: binder layer 4: noble metal particles 5: binder 6: inorganic oxide particles
11: Reaction vessel
12: Catalyst installation section
13: Glass wool
14: Catalyst fixed base (mesh structure)
15: Thermocouple installation tube

Claims (9)

  (A) Carbon nanotube carrying at least one kind of noble metal particles or noble metal oxide particles selected from the group consisting of Ag, Ru, Rh, Pd, In, Os, Ir and Pt, and (B) hydration of inorganic oxide A catalyst precursor dispersion liquid comprising a product.   (A) Carbon nanotube carrying at least one kind of noble metal particles or noble metal oxide particles selected from the group consisting of Ag, Ru, Rh, Pd, In, Os, Ir and Pt, (B) Inorganic oxide hydration And (C) a catalyst precursor dispersion comprising at least one inorganic compound particle selected from the group consisting of alumina, silica, titania, zirconia and ceria-zirconia.   A catalyst obtained by drying and calcining the catalyst precursor dispersion according to claim 1.   A catalyst, wherein the catalyst precursor dispersion according to claim 1 or 2 is coated on a carrier and then calcined to burn off carbon nanotubes.   The catalyst according to claim 4, wherein the carrier is made of metal.   The catalyst according to claim 5, wherein the metal carrier has an inorganic oxide on the surface.   The catalyst according to claim 5 or 6, wherein the metal support is stainless steel containing aluminum.   The catalyst according to any one of claims 5 to 7, wherein the shape of the support is a wire mesh.   An exhaust gas purification method using the catalyst according to any one of claims 3 to 8.